The environmental regulations are getting harder and harder with regards to deposition and destruction of dredged material and there is therefore an increased demand for fast and effective dewatering of dredged materials from harbours, channels, cool ponds, settling basins etc. The flow from dredged contents generally contains 1-10% dry substance rate and the present invention relates to facilities which can remove clean water and increase the dry substance rate to 10-30%. The dewatered dredged material can afterwards either be deposited or proceed to further processing.
It is of course advantageous the more cubic meters per hour that can be dewatered and the lower the costs for performing the dewatering can be kept. In order to make it possible to process a large flow, it is important to get a quick flocculation of the impurities and a quick sedimentation of the flocculated impurities. It is therefore advantageous if the flocculate chemicals can be mixed with the contaminated water quickly and effectively. This can be achieved by mixing the contaminated water and the flocculation chemicals under high turbulence. It is, however, also advantageous if the water subjected to turbulence can be stilled quickly in a sedimentation zone to make the flocculated contamination sink to the bottom of the sedimentation zone.
It would also be advantageous to avoid to the greatest extent possible the use of expensive and perhaps even environmentally hazardous chemicals and to keep the amount of additives as low as possible. Further, it is also an advantage if the manufacturing costs for dewatering arrangements can be kept low, that they are robust and that they can be run with as few interruptions as possible.
A further advantage would be to have the dewatering facility easily movable. For example, when the dredged materials from a contaminated harbour are dewatered it could be moved to the next contaminated harbour. This reduces the risk for the dewatering facility to be idle and at the same time makes it possible to dewater in places where it would not otherwise be an economical possibility.
It is also an advantage the lower the manufacturing costs are and that the costs of running can be kept as low as possible.
U.S. Pat. No. 7,001,525, U.S. Pat. No. 5,730,864, U.S. Pat. No. 7,014,776 are examples of constructions for purifying water, where a sedimentation zone is being used.